mysql database not updating when I access Java servlet from android

I have been creating an android app. I designed a signup form . Here when people click the signup button the details are added to the mysql table(contains confirmation code as a field.) and the confirmation code is initially set to NULL and then a servlet is called . This servlet contains the code that generates a 4 digit random number and adds it to the mysql table for the particular entry. Then the servlet calls a method in another class that sends confirmation email to the user with the code.

Now when I run the app and servlet a confirmation code is generated and it is sent to the user vie email. But the problem is the mysql table is not getting updated. Note: The code for updation of mysql table is given above the code that send email. However the same servlet updates the mysql table and sends email on submission of a HTML form.

Don't know how to solve this.. For info I am hosting the application on Amazon Elastic Beanstalk.

This is the Servlet part:

protected void processRequest(HttpServletRequest      request,HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    System.out.println("fdsfsdf");
    mBean = new MailSenderBean();
        Random n=new Random();
        int no=n.nextInt();
        no%=10000;
        if(no<0)
        {
            no=-no;
        }
        String code="0000"+no , name = request.getParameter("name"), email = request.getParameter("email");
        code=code.substring(code.length()-4, code.length());
        try{
            Class.forName("com.mysql.jdbc.Driver");
            Connection con = DriverManager.getConnection(AppConfig.dbUrl,AppConfig.dbUname, AppConfig.dbPwd);
            PreparedStatement pst=con.prepareStatement("update signup_users set code=\'"+code+"\' where name=\'"+name+"\'");
            pst.execute();
            mBean.sendMail(name, email, code);
            System.out.println("name="+name+",email="+email+",code="+code);
        }catch(Exception e)
        {
            System.out.println(""+e);
        }
    }

and my client side code in android app is

    DefaultHttpClient httpClient  = new DefaultHttpClient();
    HttpPost httpPost = new HttpPost(AppConfig.serverUrl);
    List lst =new ArrayList();
    lst.add(new BasicNameValuePair("name", name));
    lst.add(new BasicNameValuePair("email", email));
    httpPost.setEntity(new UrlEncodedFormEntity(lst));
    HttpResponse httpResponse = httpClient.execute(httpPost);